The harm of SO2, as a severe problem of the environmental pollution, has been highly focused on by the governments and the environmental protection organizations throughout the world. The SO2 pollution control technologies can be classified into three categories according to the processes as follows: pre-combustion desulfurization, oxy-fuel desulfurization and post-combustion desulfurization (also called as Flue Gas Desulfurization, abbreviated as FGD). Among others, the flue gas desulfurization is the only desulfurization manner commercialized in industrial scale up to now, and is recognized as the predominant means to control most effectively the SO2 contamination. However, the flue gas desulfurization processes currently in tests or applications are generally encountered with the technical or economic problems of possessing complex processing procedures, high equipment investment or operation cost, low removal efficiency of SO2 from the flue gas, difficult treatment and/or utilization of the byproducts and the like, and thus cannot be effectively spread widely.
Since 1980s, the exploration of new flue gas desulfurization process with advanced technology and economic cost has been always one of the hot studies in the environmental protection field. Microorganisms can be used for flue gas desulfurization, wherein the metabolic process of SO2 by chemoautotrophic microorganisms is used to remove the oxides of sulfur from flue gas. Such a process has the advantages of low operation cost, simple devices, low nutritional requirement as the autotrophic microorganisms are used, and the avoidance of secondary pollution. Therefore, the biological flue gas desulfurization is a technically novel biotechnology with high applicability, and thus has attractive prospect and potential.
Currently, the devices for the biological purification of waste gas comprise mainly three types: biological filter (BF), biological scrubber (BS) and biomembrane trickling filter (BTF). Biomembrane trickling filter is an intermediate processing technique between the biological filter and the biological scrubber, wherein the liquid phase of the biomembrane trickling filter flows continuously or flows in batches, and the microbial community is immobilized on the filtration bed, so that the adsorption of contaminants and biodegradation occur concurrently in one same reactor. Among the existing biological waste gas treatment processes, the bio-trickling filtration is the most promising one, having the advantages of easy operation, low investment and operation cost, pH-adjustable, fitting for the medium concentration of waste gas, being capable of adding with nutrient substance and the like.
Packing is the carrier of the microorganism in a biomembrane trickling filter, and is the primary location for the biological immobilization and contaminant disposal. The characteristics of the packing affect directly the growth of biomass in the packing layer, the energy consumption of the system, and the mass transfer process of odor contaminants in the gas-liquid-solid triphases and the distribution coefficient thereof. Therefore, the characteristics of the packing affect directly the treating efficiency of the biomembrane trickling filter. According to the adsorption theory, the packing should be selected with large specific surface area, good bio-affinity, acid resistance, alkali-resistance, oxidation resistance, long performance life, light weight, great mechanical strength, an installation and maintenance convenience, and cheap cost. The preferable packing increases the microorganism concentration per unit volume within the reactor, and the mass transfer of the contaminants to the microorganism, so as to enhance the systemic processing capacity, buffering capacity and system loading.
Currently, the conventional bio-packing useful for a biomembrane trickling filter is generally an inert packing, for example: rock wool-compost, zeolite, hybrid packing, light ceramsite, usually a silicate mineral or organic polymer, bearing negative charges by itself. Moreover, the packing has the disadvantages of high cost, high energy consumption, low mechanical strength, poor abrasion resistance and the like. Meanwhile, as the roughness of the packing surface is insufficient, the microorganism is difficult to be attached onto the packing surface in a short time, leading to the phenomenon of a long term of biomembrane colonization, easy slough of the biomembrane, which is unfavorable for the growth and propagation of the microorganism, and poor performance of the membrane, resulted from the existing packing.
Therefore, the modification on the packing surface of the polymeric material is particularly very necessary. It is generally considered that a packing with relatively weak adsorbability can be greatly improved for the adsorbability after modification. The modification technology has been gradually known by the artisans in the recent decade, wherein the fundamental theory for modifying a packing is to change the physicochemical properties of a packing or the surface thereof, and has been well studied in waste water treatment. It is indicated that the physical and chemical properties of the packing surface coating affecting the removal of the particles and the dissolved substance, the large specific surface area of the coating, adsorption sites on the surface, the surface roughness and the porosity bring the advantages of the modified packing.
It is recently focused on the study of flue gas desulfurization by microorganism to use a biomembrane trickling filter as the desulfurization reactor. Regarding a bio-trickling filtration, the biomembrane attached on the packing is the principle section of the reactor. The removal of contaminants depends primarily on the action of the biomembrane grown on the carrier, wherein the characteristics of the biomembrane will affect the conversion of contaminants. Meanwhile, the attaching and growing characteristics of the microorganisms on the packing surface are associated with the physical and chemical properties of the packing. The currently used bio-trickling filtration processes have generally the disadvantages of low desulfurization efficiency, a long period of biomembrane colonization, poor stability of the desulfurization efficiency and the like.